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[InstCombine] Don't fold select(C, Z, binop(select(C, X, Y), W)) -> select(C, Z, binop(Y, W)) if the binop is rem or div.

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The select may have been preventing a division by zero or INT_MIN/-1 so removing it might not be safe.

Fixes PR36362.

Differential Revision: https://reviews.llvm.org/D43276

llvm-svn: 325148
This commit is contained in:
Craig Topper 2018-02-14 18:08:33 +00:00
parent 5f83290ecf
commit 2e34d16069
2 changed files with 34 additions and 2 deletions
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19
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -1760,11 +1760,25 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
}
}
auto canMergeSelectThroughBinop = [](BinaryOperator *BO) {
// The select might be preventing a division by 0.
switch (BO->getOpcode()) {
default:
return true;
case Instruction::SRem:
case Instruction::URem:
case Instruction::SDiv:
case Instruction::UDiv:
return false;
}
};
// Try to simplify a binop sandwiched between 2 selects with the same
// condition.
// select(C, binop(select(C, X, Y), W), Z) -> select(C, binop(X, W), Z)
BinaryOperator *TrueBO;
if (match(TrueVal, m_OneUse(m_BinOp(TrueBO)))) {
if (match(TrueVal, m_OneUse(m_BinOp(TrueBO))) &&
canMergeSelectThroughBinop(TrueBO)) {
if (auto *TrueBOSI = dyn_cast<SelectInst>(TrueBO->getOperand(0))) {
if (TrueBOSI->getCondition() == CondVal) {
TrueBO->setOperand(0, TrueBOSI->getTrueValue());
@ -1783,7 +1797,8 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
// select(C, Z, binop(select(C, X, Y), W)) -> select(C, Z, binop(Y, W))
BinaryOperator *FalseBO;
if (match(FalseVal, m_OneUse(m_BinOp(FalseBO)))) {
if (match(FalseVal, m_OneUse(m_BinOp(FalseBO))) &&
canMergeSelectThroughBinop(FalseBO)) {
if (auto *FalseBOSI = dyn_cast<SelectInst>(FalseBO->getOperand(0))) {
if (FalseBOSI->getCondition() == CondVal) {
FalseBO->setOperand(0, FalseBOSI->getFalseValue());

17
test/Transforms/InstCombine/pr36362.ll Normal file
View File

@ -0,0 +1,17 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
;RUN: opt -instcombine -S %s | FileCheck %s
; We shouldn't remove the select before the srem
define i32 @foo(i1 %a, i32 %b, i32 %c) {
; CHECK-LABEL: @foo(
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[A:%.*]], i32 [[B:%.*]], i32 -1
; CHECK-NEXT: [[REM:%.*]] = srem i32 [[C:%.*]], [[SEL1]]
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[A]], i32 [[REM]], i32 0
; CHECK-NEXT: ret i32 [[SEL2]]
;
%sel1 = select i1 %a, i32 %b, i32 -1
%rem = srem i32 %c, %sel1
%sel2 = select i1 %a, i32 %rem, i32 0
ret i32 %sel2
}